While taking off for parachute dropping operation, directional control was lost and the aircraft ground looped. The left main landing gear collapsed, substantially damaging the aircraft. All six occupants evacuated the aircraft without injury.

The pilot subsequently reported that, as take-off power was applied, the aircraft started to swing to the left. He applied right rudder to correct the swing, but the aircraft then swung rapidly to the right. He was unable to counteract the swing and closed the throttle to stop the take-off. However, the left wheel ran into a culvert and was torn off before the aircraft could be stopped.

The pilot reported that he was conducting a practice forced landing when the engine stopped. At 3,000 ft he had applied full carburettor heat, closed the throttle and commenced a glide descent. During the descent he applied power on four occasions to re-warm the engine. At about 600 ft AGL the engine stopped along with the geared wooden propeller. The pilot carried out trouble checks and declared a Mayday. He twice engaged the starter in an attempt to restart the engine but was unsuccessful. He subsequently reported that the starter seemed to be sluggish.

The aircraft touched down in a paddock on a downhill slope. It rolled about 30 metres, crashed through a farm fence, passed under a powerline, crossed a road, encountered a ditch and overturned.

At the time of the accident weather conditions were: CAVOK, outside temperature about 15 degrees Celsius, wind calm, visibility 10 km plus, nil precipitation.

This was the second accident to VH-IDB in the same area due to the engine stopping during practice forced landings. The previous accident occurred on 14 May 1997. Verbal reports of other instances have been received of Skyfox Gazelles experiencing engine stoppages after the throttle was closed and engine RPM reduced to idle.

After the first accident, the engine was inspected by a licensed aircraft maintenance engineer (LAME). Then, after the second accident with the same engine installed, it was inspected first by the LAME and then by the engine manufacturer's agent. No fault was found with the engine after each accident. Post accident tests on the starter, the battery and the engine have failed to detect a reason for the sluggish starter anomaly reported by the pilot.

Safety Action

As a result of complaints about the stalling of engines at idle, Airworthiness officers from the Civil Aviation Safety Authority (CASA), in conjunction with the aircraft manufacturer, conducted an investigation which included test flights in the Gazelle.

It was found that the throttle mechanism had enough free play (also known as backlash) to reduce RPM below idle and stop the engine. This could occur if extra force was applied when pulling the throttle back to idle speed. To address this problem, the aircraft manufacturer issued Service Bulletin (SB) No. 20 on 28 October 1997. This SB provides the following information: "Idle speed may inadvertently be reduced below set minimum due to incorrect throttle stop adjustment." SB 20 requires operators to check the idle setting and adjust for backlash at the throttle stop in the cockpit. Compliance was mandatory, within two weeks or 10 hours time in service from receipt of the SB.

VH-WNZ was conducting a training flight, and the pilot had advised the Tower of his intention to conduct a simulated engine failure after take-off. The aircraft departed on an initial assigned radar heading of 060 degrees at 1710.40 EST.

VH-OGK was assigned an IBUNA 1 Standard Instrument Departure (SID), departed at 1712.30 EST, and had been instructed to remain on Tower frequency. While turning right as per the SID to heading 180 M, OGK passed behind WNZ. Separation between the aircraft reduced to 2.5 NM horizontally and less than 500 ft vertically. The required separation was 3 NM and 1,000 ft.

Investigation revealed that the aerodrome controller (ADC) did not adequately plan the departure of three aircraft, including WNZ and OGK. An arriving aircraft led to his decision to expedite the departure of OGK, thus compromising the separation between these aircraft. The ADC's decision to retain OGK on Tower frequency until instructed to transfer delayed the opportunity for the departures controller to issue instructions to OGK to ensure separation was maintained.

The pilot stated that while hovering the helicopter at about 50 ft over a dry riverbed, the engine note suddenly changed. He checked the instrument indications which confirmed that the engine RPM had increased. Almost immediately the indications returned to normal. He began to move the helicopter away from trees when the engine RPM again increased as drive to the main rotor system was lost.

During the attempted autorotational landing, the helicopter collided with a tree and landed heavily on the riverbank.

While vacating the helicopter, the pilot became aware of a "rumbling" noise and smoke coming from under the cabin. He attempted unsuccessfully to locate the source of the noise by isolating the electrical systems. He then switched off the battery.

Output from the helicopter engine is coupled through a V-belt drive system to the main transmission which drives the main rotor, and to the tail rotor drive system. The belt drive clutch control installation includes a linear actuator and electrical connections to a clutch control switch and warning light on the instrument panel. A cable and pulley interconnect the linear actuator to the clutch spring on the belt drive transmission. The clutch control switch, which is positioned on the lower left side of the instrument panel, has three positions, RELEASE, HOLD and ENGAGE (the normal operating position). With the switch in the ENGAGE position, the linear actuator retracts, applying tension through an idler pulley to the V-belts. The clutch warning light is on unless the clutch is fully engaged.

Examination of the helicopter rotor drive system did not identify any pre-existing defect which may have contributed to the accident.

The "rumbling" noise heard by the pilot was caused by the starter motor operating due to impact damage to the solenoid. There was no fire.

The linear actuator shaft was found to be extended by approximately 30 to 50% of its travel. It is normally fully retracted when the drive belts are correctly tensioned. The actuator, the clutch control switch, the clutch warning light and the associated wiring were tested and found to be serviceable. It was not possible to determine if the warning light was powered at the time of impact. The position of the linear actuator shaft may have changed following the accident when the pilot repositioned various switches and circuit breakers in an attempt to identify the "rumbling" noise.

The clutch control switch was fitted with a guard to prevent inadvertent operation. However, the retaining springs had weakened such that the guard was ineffective.

The circumstances of the accident are consistent with loss of rotor drive due to insufficient drive belt tension. However, the circumstances in which this occurred could not be determined.

The hot air balloon had taken off from Picton on an early morning joy flight to Camden. Surface wind conditions were calm, with a south-westerly wind of 24 kt at 1,000 ft. Surface winds were not expected to increase before late morning.

The pilot in command reported that the flight proceeded as planned, and a normal approach was made for a landing on Camden aerodrome. The surface wind was 5-8 kt. Some 200 m from the landing point, at a height of about 50 ft, the rate of descent began to increase more than required. The pilot activated two burners for about 5 sec to arrest the descent. As expected, the balloon flew level for a short distance, then unexpectedly began to climb rapidly. The parachute valve was opened to counteract the climb, which stopped at about 200-250 ft. However, the balloon then began to descend rapidly. All burners were turned on in an attempt to arrest the descent, but to no avail. The balloon impacted the ground at an estimated rate of descent of 600-700 fpm.

The rapid deflation system was operated just before impact, but the balloon was dragged across the ground for about 30 m before becoming airborne again, reaching a height of about 20 ft before again contacting the ground and being dragged a further 40 m. As the balloon came to a halt the pilot reported that the deflated envelope flapped in the breeze for some time, suggesting an increase in the surface wind.

One lady sustained a fractured ankle during the landing. The other twelve occupants were uninjured.

FACTUAL INFORMATION

Background

The pilot/owner of VH-CSW had been approached some time before the accident with a request to allow passengers to abseil from his helicopter while it was in a hover. The pilot approached a Civil Aviation Safety Authority (CASA) representative who advised the pilot that he would need to submit a proposed amendment to the company's Operations Manual detailing how such flights would be conducted. The representative also advised that any proposed amendment would have to be approved by CASA before any such flights could be conducted and that the representative had already approached a CASA helicopter specialist to discuss safety aspects of the proposed flights.

Because of the CASA requirement for a detailed proposal for conduct of the proposed flights, the pilot decided to conduct some controllability tests prior to submitting his proposed Operations Manual amendment. Because the pilot declined to be interviewed or to supply the investigation with a statement, it is not known whether he conducted any calculations into the lateral centre of gravity (cg) implications of the proposed flights.

The pilot positioned the helicopter to a helipad near the accident site on the morning of the accident and carried out some local flights prior to the accident flight. Another helicopter pilot, who had flown for the company on a casual basis in the past, drove to the area with addition fuel for the day's planned flights.

A briefing was conducted by the pilot to explain how he proposed to conduct the experimental flight. Present at that briefing were the passenger, who had accompanied the pilot to the site in the helicopter that morning and who had an interest in the proposed abseiling flights, the casual helicopter pilot and another local person. A fourth person was also present at the scene but did not attend the briefing.

The proposed flight discussed at this briefing required that an abseiling rope be attached to the outside of the front cross-tube of the skid assembly of the helicopter and that one passenger be seated in the right seat of the helicopter. The rope would be attached in such a manner that it hung over the outside edge of the right skid tube. The pilot then intended to lift the helicopter to a hover about 10 m above the helipad and the casual pilot was briefed to walk under the hovering helicopter and to gradually apply his weight onto the abseiling rope. One of the persons briefed earlier had radio communication with the pilot through a hand-held radio transceiver.

History of the flight

The flight proceeded as planned initially and the pilot was able to remain in control of the helicopter with one person, the other pilot, who weighed about 70 kg, suspended by the abseiling rope. The person at the helipad stated that the pilot then contacted him by radio and asked that the other person standing there (who had not attended the briefing) also put his weight on the rope. That spectator quickly moved under the helicopter and applied his weight, reportedly about 80 kg, onto the rope.

The helicopter rolled rapidly to the right and began to go out of control. When it became evident to the persons on the rope that the pilot could not control the helicopter with both their weights applied, they both quickly let go and attempted to move away from under the helicopter. Although the casual pilot managed to get clear, the other person's ankle became entangled in the rope and he was lifted by the helicopter as it banked steeply right, (now out of control), and it proceeded to pivot 180 degrees to the right and move across the road towards a small service station, dragging the person below it by the leg.

One of the helicopter's main rotor blades struck the steel upright of a large illuminated sign; the helicopter then descended and struck the rear of a vehicle parked in front of the service station. The helicopter landed heavily beside this vehicle with its tail boom broken off but with its engine still running and main rotor still turning, causing major damage to the vehicle and multiple blade strikes to the building.

The pilot was winded in the accident, partly because the shoulder harness section of his inertia reel seatbelt had failed on impact. He managed, with some difficulty, to activate the emergency fuel cut-off to shut down the engine after unsuccessfully attempting to stop the engine by switching off the magnetos.

Spectators arrived to assist the pilot and passenger from the severely damaged cabin and to extinguish a fuel fire that had started below the ruptured left fuel tank.

The two occupants of the helicopter and the person caught by the leg by the abseiling rope all received minor injuries. The helicopter was destroyed and severe damage was caused to the service station buildings and the vehicle parked in front of the office. Although there were persons in the buildings when the helicopter crashed, none of them were injured.

The aircraft

The helicopter had been manufactured in 1970 and its data plate identified it as a Bell 47G-3B-2. It had been converted some time later to a Bell 47G-2A-1, although registration records show the type as a Bell 47G-3B-1.

Examination of the aircraft at the accident site and a search of maintenance records proved that the aircraft was suitably registered and that the maintenance release was current. No defects that would have affected the flight were apparent. The failed pilot's shoulder harness inertia reel was recovered for failure analysis.

The pilot was suitably licensed and endorsed on the aircraft type.

ANALYSIS

The Flight Manual for the helicopter type did not cover abseiling operations and there was no procedure for the attachment of ropes or lifting devices to the skid tubes in the manner used on the accident flight. There was no centre of gravity (cg) chart provided in the manual for loads attached to the skids. In normal operations, any loads that are to be suspended below the helicopter are attached to the purposely installed cargo hook mounted under the helicopter close to the cg. CSW was fitted with such a device which has both electrical and mechanical methods for instantly releasing the load when required, especially in an emergency.

The forward skid cross tube was about 780 mm forward of the optimal longitudinal centre of gravity and any load applied on a rope attached to it would cause the helicopter to pitch nose-down as well as causing it to roll to the right.

The Flight Manual for the Bell 47G series of helicopter has a section on loading of cargo litters (if installed) which states that the maximum load allowable on a litter is 102 kg. Litters are mounted fore-and-aft on the skid cross-tubes between the cabin side and the outside of the skid. An asymmetric loading chart is provided with the litter kit and is used for calculation of maximum allowable difference between loads on the left and right litters. As an example of the sensitivity of this type of helicopter to asymmetric lateral loads, if there is a passenger of 75 kg in the right seat, it is only possible to carry about 55 kg more on the right litter than on the left to remain inside allowable lateral cg limits. As the outside of the skid tube is several centimetres outboard of the litter centreline, any load applied at the skid tube would have a greater adverse effect on the lateral cg than the same load on a litter.

On the accident flight, the pilot was simulating an asymmetric load of about 150 kg (no load on the left skid tube, two persons hanging from the right skid), attached to the helicopter in such a manner that the lateral cg limits imposed by the manufacturer were exceeded. This lateral cg exceedance combined with a pitch-down of the nose as the load was applied, resulting in a loss of control.

The carriage of a passenger of about 80 kg in the right seat would have resulted in the helicopter being close to a laterally balanced condition before any load was applied to the rope. If it had been decided to conduct a proving flight after calculation of the lateral cg implications, the conditions would have been better simulated with no passengers in the cabin or with one occupying the centre seat. It would be expected that the person from the right seat would have been the one abseiling from the helicopter. A seating configuration which left the right seat empty would have reduced the exceedance of lateral cg experienced on the accident flight.

The two persons applying their weight to the rope attached under the helicopter released their hold when they realised the helicopter was not maintaining a steady hover. As one of the persons stepped backwards, his ankle became entangled in the rope. He was lifted by the helicopter then dragged up a bank onto a road. This dragging load, which could not be released from the aircraft in an emergency, probably prevented the pilot from regaining control before the helicopter struck the sign.

Although abseiling from helicopters is frequently carried out in military operations, the aircraft used are normally larger, cabin-class helicopters and it is possible for persons abseiling from the helicopter to do so from each side simultaneously, thus reducing the risk of an exceedance of lateral cg limits.

Investigation into the failure of the pilot's shoulder harness inertia reel revealed that the unit fitted to the helicopter was not approved for installation in Bell 47G aircraft type.

SIGNIFICANT FACTORS

The pilot was attempting to explore the effect on helicopter control of a lateral load applied to the outside of the right skid tube.

The lateral centre of gravity limitations of the helicopter were exceeded, resulting in loss of control.

The pilot was unable to regain control before impact with a sign when a person became entangled in the rope attached to the helicopter.

The pilot was tasked with flying passengers from Port Augusta to Cook, via Ceduna. After arriving at Cook the aircraft was flown without passengers to Nullabor for an overnight stop. The following day, he was to return to Cook to collect a group of eight passengers and fly them to Port Augusta. The aircraft had been refuelled to full capacity at Ceduna on the flight out to Cook. During this refuelling the pilot did not note the amount of fuel used on the flight from Port Augusta. The pilot calculated that the fuel remaining at Cook for the return flight would be 439 litres. He also calculated that the fuel required to return to Port Augusta from Cook would be 452 litres. This fuel requirement was calculated using a fuel flow of 140 litres per hour and a true airspeed of 170 knots with a 15-knot headwind. The fuel requirement included a 100-litre fixed reserve. The pilot was aware that there was a 13-litre shortfall between the fuel on board and the fuel required. He did not eliminate this discrepancy by adding fuel at Nullarbor where it was available. The weight of the aircraft on departure from Cook was calculated by the pilot as being 35 kg below maximum take-off weight. However, this calculation was based on 423 litres of fuel, rather than 439 litres.

The aircraft departed Cook at 0007 UTC and the pilot passed an estimate with his departure report of abeam Ceduna at 0116. The aircraft reported abeam Ceduna at 0116 and gave an estimate to flight service for Port Augusta of 0238. This estimate gave a time interval which was 9 minutes longer than planned by the pilot. The pilot had submitted a flight plan to ATS that indicated a groundspeed of at least 165 knots would be achieved during the flight. The pilot had planned the flight expecting the true airspeed to be higher, and therefore the groundspeed to be higher, on the return flight. He also expected to obtain favourable winds at various altitudes and therefore did not plan to use the reserve fuel of 100 litres. He also assumed that he would obtain a better fuel flow than the 140 litres per hour that he had used during the planning for the flight. The flight progressed uneventfully until approximately 90 nm from Port Augusta when the pilot noticed that the fuel remaining on board had decreased to a lower level than expected. He elected to divert to Wudinna as he was now in some doubt as to whether the aircraft would make Port Augusta with the fuel remaining on board.

The decision to divert to Wudinna was based on the fact that the company held fuel stocks at this location. He advised flight service that he was diverting due to a higher-than-normal fuel burn. Flight service declared an alert phase at this time due to the pilot reporting 20 minutes endurance with a time interval to Wudinna of 10 minutes. En-route to Wudinna the pilot noticed that the airfield was situated beyond a heavily timbered area and he elected to carry out a precautionary search-and-landing in a cleared paddock whilst there was fuel remaining, rather than continue over the timbered area where he might suffer fuel exhaustion. The pilot advised flight service that he was carrying out a precautionary landing and they declared a distress phase due to the unsure fuel status of the aircraft. The pilot completed the precautionary search-and-landing without damage to the aircraft or injury to the passengers. The position of the precautionary landing was 19 nm north-east of Wudinna. The company was advised, and the aircraft was recovered to Wudinna later that day.

The estimated fuel remaining on board was less than 30 litres. In his report to the Bureau as part of the investigation, the pilot indicated that he operated the aircraft during both the outbound flight to Cook and the return flight to Port Augusta using fuel flow and exhaust gas temperature (EGT) settings from another company aircraft. These settings had resulted in an actual fuel flow of approximately 165 litres per hour.

Significant Factors

1. The pilot used a fuel flow setting during flight planning that was not representative of that which the aircraft would achieve during flight.

2. The pilot departed from an aerodrome where fuel was available knowing that the fuel on board was less than that required for the flight, with reserves.

The pilot was conducting circuits to gain familiarization with the aircraft. Late in the landing roll he encountered a willy-willy, which caused the aircraft to swing. Using right brake, the pilot was unable to control the swing, and the right wheel assembly broke off. The right wing fell to the ground and the pilot exited the aircraft when it stopped.

The aircraft was not fitted with an electronic locator beacon.

FACTUAL INFORMATION

History of the flight

The pilot was undergoing a flight test for the initial issue of a multi-engine command instrument rating under the supervision of an Air Test Officer (ATO). The ATO was the owner, chief pilot, and chief flying instructor of the flying training school with which the private pilot was undertaking his training. He had been working long hours and had not taken a holiday for at least a year. 

The flight was from Archerfield to Kilcoy, Maroochydore, Brisbane, then return to Archerfield. Although a flight plan had been submitted, no contact with the controllers at Maroochydore had been made in order to arrange for the instrument approach training.

Some aerial work was conducted in the Kilcoy area prior to tracking to Maroochydore. At some point around, or shortly after leaving, Kilcoy the ATO fell asleep. When the aircraft was about 22 NM from Maroochydore the pilot under test made a position report and requested an airways clearance. He was instructed to track overhead Maroochydore at 4,000 ft and make a sector entry. Since the normal commencement altitude for an approach at Maroochydore was 3,000 ft, the controller was expecting the pilot to report overhead when ready to descend to 3,000 ft in preparation for an instrument approach.

The controller saw the aircraft east of the control tower after it had passed overhead. He anticipated that the pilot would soon request descent for the approach and had cleared other aircraft in such a way as to keep the airspace free for the approach. He did not speak to the pilot as he was aware that aircraft on instrument training can sometimes conduct operations in the holding pattern for some time before requesting an approach. After arriving over Maroochydore the pilot under test conducted the planned instrument approach. When the aircraft was about half way through the approach and turning inbound towards the aerodrome the ATO woke up. As the aircraft was then at the point in the approach at which he intended simulating an engine failure for the pilot under test, the ATO did this without comment.

The next transmission from the aircraft occurred on final approach for runway 18 when the pilot requested a landing clearance. The controller questioned how the aircraft had progressed to that point but issued a landing clearance and a clearance to continue the planned flight. The ATO deduced that the aircraft had descended without a clearance.

A few minutes prior to the pilot's request to land an aircraft had departed from runway 12 at Maroochydore and had turned left to track to the north-west to the training area. Since the controller was not aware of the presence of the aircraft so close to the circuit area, no separation standard had been applied to the departing aircraft. By coincidence, it is likely that the aircraft did not conflict.

Personnel information

The ATO held a commercial pilot licence with a current medical certificate. He claimed a total flying experience of 8,300 hours, and he had flown 20 hours during the month of the incident. He had been working at least six days a week for more than a year. Although he considered that his flight crew duty times did not contravene the current regulations, this calculation did not involve the additional time spent in managing the flying school.

The ATO said that for about four weeks prior to the incident he had been suffering from influenza but had not seen a doctor or taken himself off flying duties. He considered that his presence at work, and his flight test duties, were necessary in order to maintain the success of the business. He indicated that he had fallen asleep briefly on previous flights. Following the subject incident he had attended a doctor who informed him that he was suffering from bronchitis.

An accurate assessment of the pilot's activities and food intake in the days leading to the incident could not be made as the pilot could not remember his activities nor his meal intake. He had commenced work at 0800 on the day of the incident and other days had been unremarkable as far as his normal routine was concerned.

ANALYSIS

At the time of this incident the pilot under test was expected to be able to conduct the flight as a single pilot operation. His failure to obtain a clearance for the approach is considered a factor.

The ATO did not notice the failure to obtain a descent / approach clearance because he was asleep. He was suffering from fatigue and an illness. This is considered a factor.

The controller had observed the aircraft overhead at an appropriate time and therefore had no need to request position information from the pilot. He was anticipating a request for descent from the pilot and did not intend prompting the pilot unless the request was well overdue.

The ATO considered that he complied with the existing flight crew duty limitations if only his flying activities were considered. He considered that he was not within those limitations if his business work was considered. While flying can be a cause of an increase in fatigue, a person's fatigue state is determined by the total consideration of a person's waking / sleeping cycles and total activity. In this case, if the person's total lifestyle had been considered, he would not have been flying.

SIGNIFICANT FACTORS

1. The pilot in command fell asleep due to fatigue and illness.

2. The pilot under test conducted a descent and approach without a clearance.

SAFETY ACTION

The interpretation and application of flight and duty times has been raised as a safety concern in previous investigations and safety studies. More recently, the Bureau conducted a study of the safety of Australian regional airlines. The need for an understanding of, and pragmatic approach to, fatigue management principles was highlighted in that study. Safety action relating to this issue is currently being drafted.

FACTUAL INFORMATION

A Shorts SH36 aircraft had departed Williamtown on a flight to Brisbane. The crew were maintaining the aircraft at 9,000 ft outside controlled airspace and were in contact with Flight Service Area 5 (FIS 5).

A Dash 8 aircraft had departed Sydney on a flight to Taree. The crew were maintaining the aircraft at flight level (FL) 150 and were under the control of Brisbane Sector 15C.

The sector controller coordinated the overhead Williamtown position of the Dash 8 with FIS 5. This coordination included an estimate for Taree and advice that the crew would contact FIS 5 at "top of descent".

The flight service officer correctly calculated that the two aircraft would be in conflict and passed traffic information on the Dash 8 to the crew of the SH36. Although aware of a requirement to back coordinate with sector control when an aircraft leaving controlled airspace on descent required traffic information, the officer elected not to pass the information to the sector controller. She had calculated that there would be at least 3 minutes between the top of descent of the Dash 8 and the aircraft coming into conflict and therefore sufficient time for her to pass the traffic information to the crew.

The crew of the Dash 8 were cleared to leave controlled airspace on descent to Taree and were instructed to contact FIS 5 by sector control, immediately after they reported leaving FL150. They attempted to do this but were delayed by other airspace users transmitting on that frequency. They finally made their broadcast while passing 13,000 ft and at a rate of descent of 1,800 ft/min. The base of controlled airspace in the Taree area was 12,500 ft. The Aeronautical Information Publication required a crew to make their first broadcast on the flight information service frequency prior to leaving controlled airspace.

The flight service officer acknowledged the transmission from the crew of the Dash 8 and passed the traffic information on the SH36 and two other aircraft. By the time the crew had analysed this information and assessed that the SH36 was in direct conflict, their aircraft was passing between 11,000 ft and 10,500 ft. The pilot in command immediately amended the altitude selection to 10,000 ft and the automatic pilot commenced the level-off manoeuvre at 10,400 ft. The aircraft levelled off at 10,000 ft and the crew saw the SH36 in their 12-o'clock position. Both crews had been using Global Positioning System navigational equipment and were accurately "on track".

The two crews then established communication and mutual sighting. There was no breakdown of separation, and the crews completed a safe sighting and passing manoeuvre.

ANALYSIS

Analysis of the respective flight paths indicated that the aircraft avoided a direct conflict by approximately 30 seconds. Both crews agreed that their respective aircraft were on-track and the position of the SH36 was such that the closing speed and descent profile of the Dash 8 could have resulted in a mid-air collision had the rate of descent not been arrested.

The level-off of the Dash 8 was implemented as soon as the crew had analysed the position of the SH36 and before they achieved visual contact. Had they been delayed further in their attempts to contact FIS 5, the separation would have been significantly reduced.

The flight service officer had received the correct coordination from the sector controller and made a correct assessment of the conflict. However, her decision not to bother air traffic control with the need to pass traffic information was predicated on an assumption that the crew of the Dash 8 would call her at top of descent. If such a call was made, it would have given her more than 3 minutes to carry out the broadcast and this would probably have been sufficient for the task. However, such a timely call could not be guaranteed and on this occasion did not happen. The resultant delay reduced the time available for the crew to make an informed judgement about the traffic.

The phrase "top of descent" was used by the controller to indicate a transfer of the aircraft to FIS 5 as soon as practicable after the crew reported leaving their cruising level. The regulations allowed the crew to report vacating a level up to 1 minute after the event. A further delay in making the broadcast then occurred due to other airspace users making authorised transmissions. This delay could not be accurately estimated and was always going to be of unknown duration.

The flight service officer considered that the phrase "top of descent" meant exactly that and made an assessment based on this belief.

SIGNIFICANT FACTORS

1. The flight service officer elected not to coordinate the traffic information on the SH36 to the crew of the Dash 8 with Sector Control.

2. The flight service officer expected the crew of the Dash 8 to contact her at "top of descent".

3. The crew of the Dash 8 were delayed in making the initial broadcast on FIS5 due to frequency congestion.

SAFETY ACTION

Airservices Australia Northern District Office issued a local instruction (NDO 97/191) on 29 August 1997 which specified improved procedures for the transfer of communications to flight information service frequencies when an aircraft is on descent from controlled airspace.

As a result of this and other occurrences, the Bureau of Air Safety Investigation is developing recommendations relating to the provision of timely traffic information by air traffic services and for flight crews to develop separation assurance techniques.

Any recommendations arising will be published in the Bureau's Quarterly Safety Deficiency report.